Technique for detection of line-of-sight transmissions using millimeter wave communication devices

ABSTRACT

Systems and methods for wireless communications are disclosed. More particularly, aspects of the present disclosure generally relate to techniques for wireless communications by a first apparatus comprising obtaining, via at least first and second receive antennas having different polarizations, first and second training signals transmitted from a second apparatus via at least first and second transmit antennas having different polarizations, determining, based on the first and second training signals, one or more characteristics for different transmit-receive antenna pairs, each pair comprising one of the first or second transmit antennas and one of the first or second receive antennas, and generating, based on one or more characteristics, a parameter indicative of whether a link path between the first and second apparatuses is line of sight (LOS).

CLAIM OF PRIORITY UNDER 35 U.S.C. §119

The present Application for Patent claims benefit of U.S. ProvisionalPatent Application Ser. No. 62/084,111, filed Nov. 25, 2014 and assignedto the assignee hereof and hereby expressly incorporated by referenceherein.

TECHNICAL FIELD

Aspects of the present disclosure generally relate to wirelesscommunications and, more particularly, to determining whether wirelessdevices are in a line of site (LOS) based on training signalstransmitted from one of the devices.

BACKGROUND

The 60 GHz band is an unlicensed band which features a large amount ofbandwidth and a large worldwide availability overlap. The largebandwidth means that a very high volume of information can betransmitted wirelessly. As a result, multiple applications, eachrequiring transmission of large amounts of data, can be developed toallow wireless communication around the 60 GHz band. Examples for suchapplications include, but are not limited to, wireless high definitionTV (HDTV), wireless docking stations, wireless Gigabit Ethernet, andmany others.

In order to facilitate such applications there is a need to developintegrated circuits (ICs) such as amplifiers, mixers, radio frequency(RF) analog circuits, and active antennas that operate in the 60 GHzfrequency range. An RF system typically comprises active and passivemodules. The active modules (e.g., a phased array antenna) requirecontrol and power signals for their operation, which are not required bypassive modules (e.g., filters). The various modules are fabricated andpackaged as radio frequency integrated circuits (RFICs) that can beassembled on a printed circuit board (PCB). The size of the RFIC packagemay range from several to a few hundred square millimeters.

In the consumer electronics market, the design of electronic devices,and thus the design of RF modules integrated therein, should meet theconstraints of minimum cost, size, power consumption, and weight. Thedesign of the RF modules should also take into consideration the currentassembled configuration of electronic devices, and particularly handhelddevices, such as laptop and tablet computers, in order to enableefficient transmission and reception of millimeter wave signals.Furthermore, the design of the RF module should account for minimalpower loss of receive and transmit RF signals and for maximum radiocoverage.

Operations in the 60 GHz band allow the use of smaller antennas ascompared to lower frequencies. However, as compared to operating inlower frequencies, radio waves around the 60 GHz band have highatmospheric attenuation and are subject to higher levels of absorptionby atmospheric gases, rain, objects, etc., resulting in higher freespace loss. Additionally, radio waves around the 60 GHz band are oftenreflected by environmental objects. These reflections can change thepolarity of the transmissions and this change varies depending on thedirection of the polarity of the transmission, as the reflectioncoefficients for various polarization directions can differ.

This sensitivity to environmental conditions makes determining a linkpath important. The link path describes the path the radio wave takesbetween the transmitter and receiver. The link path may include multiplepaths such as direct line of sight (LOS), reflection, diffraction,scattering and others. Unlike a radio link in lower frequencies, in a 60GHz link, reflections are the second dominant mode, right after LOS.Other modes occur significantly less frequently and are rarely selected.Determining whether a LOS connection is desirable because many wirelessdevices need a way to estimate the distance between a transmitter andreceiver. The connection mode influences this measurement because anindirect path may result in a longer measured distance than the actualdistance.

Existing techniques for determining the distance include time-of-flight(TOF), estimations of the power-delay-profile (PDP), received powerlevel, and in-room mapping. While these techniques may be sufficient fordevices operating in frequencies lower than about seven GHz, thesetechniques alone are insufficient for transmissions around the 60 GHzband. For example, for the 60 GHz band, the PDP of a reflected path canbe similar to that of a non-reflective path. Therefore, a technique fordetermining whether there is a LOS or non-LOS connection is desired.

SUMMARY

Certain aspects of the present disclosure provide a first apparatus forwireless communications. The apparatus generally includes a firstinterface for obtaining, via at least first and second receive antennashaving different polarizations, first and second training signalstransmitted from a second apparatus via at least first and secondtransmit antennas having different polarizations, and a processingsystem configured to determine, based on the first and second trainingsignals, one or more characteristics for different transmit-receiveantenna pairs, each pair comprising one of the first or second transmitantennas and one of the first or second receive antennas, and generate,based on the characteristics, a line of sight (LOS) parameter indicativeof whether a link path between the first and second apparatus is LOS.

Certain aspects of the present disclosure provide a method for wirelesscommunications. The method generally includes obtaining, by a firstapparatus, via at least first and second receive antennas havingdifferent polarizations, first and second training signals transmittedfrom a second apparatus via at least first and second transmit antennashaving different polarizations, determining, based on the first andsecond training signals, one or more characteristics for differenttransmit-receive antenna pairs, each pair comprising one of the first orsecond transmit antennas and one of the first or second receiveantennas, and generating, based on the characteristics, a line of sight(LOS) parameter indicative of whether a link path between the first andsecond apparatus is LOS.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a diagram of an example wireless communicationsnetwork, in accordance with certain aspects of the present disclosure.

FIG. 2 illustrates a block diagram of an example access point and userterminals, in accordance with certain aspects of the present disclosure.

FIG. 3 illustrates a block diagram of an example wireless device, inaccordance with certain aspects of the present disclosure.

FIG. 4 illustrates an example dual polarized patch element, inaccordance with certain aspects of the present disclosure.

FIG. 5 is a diagram illustrating signal propagation in an implementationof phased-array antennas.

FIG. 6 illustrates example operations that may be performed by awireless device for determining a parameter indicative of line of site(LOS), in accordance with certain aspects of the present disclosure.

FIG. 6A illustrates example components capable of performing theoperations shown in FIG. 6.

DETAILED DESCRIPTION

Aspects of the present disclosure provide techniques for determiningwhether wireless devices are in a line of site (LOS) based on trainingsignals transmitted from one of the devices based on relative gainand/or phase of training signals transmitted from antennas withdifferent polarizations (e.g., horizontal and vertical). Such techniquesmay provide various advantages over measurements from other techniquesand, in some cases, may be used to verify or augment such measurements.

Various aspects of the disclosure are described more fully hereinafterwith reference to the accompanying drawings. This disclosure may,however, be embodied in many different forms and should not be construedas limited to any specific structure or function presented throughoutthis disclosure. Rather, these aspects are provided so that thisdisclosure will be thorough and complete, and will fully convey thescope of the disclosure to those skilled in the art. Based on theteachings herein one skilled in the art should appreciate that the scopeof the disclosure is intended to cover any aspect of the disclosuredisclosed herein, whether implemented independently of or combined withany other aspect of the disclosure. For example, an apparatus may beimplemented or a method may be practiced using any number of the aspectsset forth herein. In addition, the scope of the disclosure is intendedto cover such an apparatus or method which is practiced using otherstructure, functionality, or structure and functionality in addition toor other than the various aspects of the disclosure set forth herein. Itshould be understood that any aspect of the disclosure disclosed hereinmay be embodied by one or more elements of a claim.

The word “exemplary” is used herein to mean “serving as an example,instance, or illustration.” Any aspect described herein as “exemplary”is not necessarily to be construed as preferred or advantageous overother aspects.

Although particular aspects are described herein, many variations andpermutations of these aspects fall within the scope of the disclosure.Although some benefits and advantages of the preferred aspects arementioned, the scope of the disclosure is not intended to be limited toparticular benefits, uses, or objectives. Rather, aspects of thedisclosure are intended to be broadly applicable to different wirelesstechnologies, system configurations, networks, and transmissionprotocols, some of which are illustrated by way of example in thefigures and in the following description of the preferred aspects. Thedetailed description and drawings are merely illustrative of thedisclosure rather than limiting, the scope of the disclosure beingdefined by the appended claims and equivalents thereof.

An Example Wireless Communication System

The techniques described herein may be used for various broadbandwireless communication systems, including communication systems that arebased on an orthogonal multiplexing scheme. Examples of suchcommunication systems include Orthogonal Frequency Division MultipleAccess (OFDMA) systems. An OFDMA system uses orthogonal frequencydivision multiplexing (OFDM), which is a modulation technique thatpartitions the overall system bandwidth into multiple orthogonalsub-carriers. These sub-carriers may also be called tones, bins, etc.With OFDM, each sub-carrier may be independently modulated with data. AnSC-FDMA system may use interleaved FDMA (IFDMA) to transmit onsub-carriers that are distributed across the system bandwidth, localizedFDMA (LFDMA) to transmit on a block of adjacent sub-carriers, orenhanced FDMA (EFDMA) to transmit on multiple blocks of adjacentsub-carriers. In general, modulation symbols are sent in the frequencydomain with OFDM and in the time domain with SC-FDMA.

The teachings herein may be incorporated into (e.g., implemented withinor performed by) a variety of wired or wireless apparatuses (e.g.,nodes). In some aspects, a wireless node implemented in accordance withthe teachings herein may comprise an access point or an access terminal.

An access point (“AP”) may comprise, be implemented as, or known as aNode B, a Radio Network Controller (“RNC”), an evolved Node B (eNB), aBase Station Controller (“BSC”), a Base Transceiver Station (“BTS”), aBase Station (“BS”), a Transceiver Function (“TF”), a Radio Router, aRadio Transceiver, a Basic Service Set (“BSS”), an Extended Service Set(“ESS”), a Radio Base Station (“RBS”), or some other terminology.

An access terminal (“AT”) may comprise, be implemented as, or known as asubscriber station, a subscriber unit, a mobile station, a remotestation, a remote terminal, a user terminal, a user agent, a userdevice, user equipment, a user station, or some other terminology. Insome implementations, an access terminal may comprise a cellulartelephone, a cordless telephone, a Session Initiation Protocol (“SIP”)phone, a wireless local loop (“WLL”) station, a personal digitalassistant (“PDA”), a handheld device having wireless connectioncapability, a Station (“STA”), or some other suitable processing deviceconnected to a wireless modem. Accordingly, one or more aspects taughtherein may be incorporated into a phone (e.g., a cellular phone or smartphone), a computer (e.g., a laptop), a portable communication device, aportable computing device (e.g., a personal data assistant), anentertainment device (e.g., a music or video device, or a satelliteradio), a global positioning system device, or any other suitable devicethat is configured to communicate via a wireless or wired medium.

FIG. 1 illustrates a system 100 in which aspects of the disclosure maybe performed. For example, the access point 110 or user terminal 120 maydetermine whether another access point 110 or user terminal 120 iscapable of receiving a paging frame (e.g., an ultra low-power pagingframe) via a second radio (e.g., a companion radio), while a first radio(e.g., a primary radio) is in a low-power state. The access point 110 oruser terminal 120 may generate and transmit the paging frame comprisinga command field (e.g., a message ID field) that indicates one or moreactions for the other access point 110 or user terminal 120 to take.

The system 100 may be, for example, a multiple-access multiple-inputmultiple-output (MIMO) system 100 with access points and user terminals.For simplicity, only one access point 110 is shown in FIG. 1. An accesspoint is generally a fixed station that communicates with the userterminals and may also be referred to as a base station or some otherterminology. A user terminal may be fixed or mobile and may also bereferred to as a mobile station, a wireless device or some otherterminology. Access point 110 may communicate with one or more userterminals 120 at any given moment on the downlink and uplink. Thedownlink (i.e., forward link) is the communication link from the accesspoint to the user terminals, and the uplink (i.e., reverse link) is thecommunication link from the user terminals to the access point. A userterminal may also communicate peer-to-peer with another user terminal. Asystem controller 130 may couple to and provide coordination and controlfor the access point.

A system controller 130 may provide coordination and control for theseAPs and/or other systems. The APs may be managed by the systemcontroller 130, for example, which may handle adjustments to radiofrequency power, channels, authentication, and security. The systemcontroller 130 may communicate with the APs via a backhaul. The APs mayalso communicate with one another, e.g., directly or indirectly via awireless or wireline backhaul.

While portions of the following disclosure will describe user terminals120 capable of communicating via Spatial Division Multiple Access(SDMA), for certain aspects, the user terminals 120 may also includesome user terminals that do not support SDMA. Thus, for such aspects, anaccess point (AP) 110 may be configured to communicate with both SDMAand non-SDMA user terminals. This approach may conveniently allow olderversions of user terminals (“legacy” stations) to remain deployed in anenterprise, extending their useful lifetime, while allowing newer SDMAuser terminals to be introduced as deemed appropriate.

The access point 110 and user terminals 120 employ multiple transmit andmultiple receive antennas for data transmission on the downlink anduplink. For downlink MIMO transmissions, N_(ap) antennas of the accesspoint 110 represent the multiple-input (MI) portion of MIMO, while a setof K user terminals represent the multiple-output (MO) portion of MIMO.Conversely, for uplink MIMO transmissions, the set of K user terminalsrepresent the MI portion, while the N_(ap) antennas of the access point110 represent the MO portion. For pure SDMA, it is desired to haveN_(ap)≧K≧1 if the data symbol streams for the K user terminals are notmultiplexed in code, frequency or time by some means. K may be greaterthan N_(ap) if the data symbol streams can be multiplexed using TDMAtechnique, different code channels with CDMA, disjoint sets of subbandswith OFDM, and so on. Each selected user terminal transmitsuser-specific data to and/or receives user-specific data from the accesspoint. In general, each selected user terminal may be equipped with oneor multiple antennas (i.e., N_(ut)≧1). The K selected user terminals canhave the same or different number of antennas.

The system 100 may be a time division duplex (TDD) system or a frequencydivision duplex (FDD) system. For a TDD system, the downlink and uplinkshare the same frequency band. For an FDD system, the downlink anduplink use different frequency bands. MIMO system 100 may also use asingle carrier or multiple carriers for transmission. Each user terminalmay be equipped with a single antenna (e.g., in order to keep costsdown) or multiple antennas (e.g., where the additional cost can besupported). The system 100 may also be a TDMA system if the userterminals 120 share the same frequency channel by dividingtransmission/reception into different time slots, each time slot beingassigned to different user terminal 120.

FIG. 2 illustrates example components of the AP 110 and UT 120illustrated in FIG. 1, which may be used to implement aspects of thepresent disclosure. One or more components of the AP 110 and UT 120 maybe used to practice aspects of the present disclosure. For example,antenna 224, Tx/Rx 222, processors 210, 220, 240, 242, and/or controller230 may be used to perform the operations described herein andillustrated with reference to FIGS. 17-18A. Similarly, antenna 252,Tx/Rx 254, processors 260, 270, 288, and 290, and/or controller 280 ofthe UT 120 may be used to perform the operations described herein andillustrated with reference to FIGS. 5-5A.

FIG. 2 illustrates a block diagram of access point 110 and two userterminals 120 m and 120 x in MIMO system 100. The access point 110 isequipped with N_(t) antennas 224 a through 224 ap. User terminal 120 mis equipped with N_(ut,m) antennas 252 ma through 252 mu, and userterminal 120 x is equipped with N_(ut,x) antennas 252 xa through 252 xu.The access point 110 is a transmitting entity for the downlink and areceiving entity for the uplink. Each user terminal 120 is atransmitting entity for the uplink and a receiving entity for thedownlink. As used herein, a “transmitting entity” is an independentlyoperated apparatus or device capable of transmitting data via a wirelesschannel, and a “receiving entity” is an independently operated apparatusor device capable of receiving data via a wireless channel. In thefollowing description, the subscript “dn” denotes the downlink, thesubscript “up” denotes the uplink. For SDMA transmissions, Nup userterminals simultaneously transmit on the uplink, while Ndn userterminals are simultaneously transmit on the downlink by the accesspoint 110. Nup may or may not be equal to Ndn, and Nup and Ndn may bestatic values or can change for each scheduling interval. Thebeam-steering or some other spatial processing technique may be used atthe access point and user terminal.

On the uplink, at each user terminal 120 selected for uplinktransmission, a transmit (TX) data processor 288 receives traffic datafrom a data source 286 and control data from a controller 280. Thecontroller 208 may be coupled with a memory 282. TX data processor 288processes (e.g., encodes, interleaves, and modulates) the traffic datafor the user terminal based on the coding and modulation schemesassociated with the rate selected for the user terminal and provides adata symbol stream. A TX spatial processor 290 performs spatialprocessing on the data symbol stream and provides N_(ut,m) transmitsymbol streams for the N_(ut,m) antennas. Each transmitter unit (TMTR)254 receives and processes (e.g., converts to analog, amplifies,filters, and frequency upconverts) a respective transmit symbol streamto generate an uplink signal. N_(ut,m) transmitter units 254 provideN_(ut,m) uplink signals for transmission from N_(ut,m) antennas 252 tothe access point.

Nup user terminals may be scheduled for simultaneous transmission on theuplink. Each of these user terminals performs spatial processing on itsdata symbol stream and transmits its set of transmit symbol streams onthe uplink to the access point.

At access point 110, N_(ap) antennas 224 a through 224 ap receive theuplink signals from all Nup user terminals transmitting on the uplink.Each antenna 224 provides a received signal to a respective receiverunit (RCVR) 222. Each receiver unit 222 performs processingcomplementary to that performed by transmitter unit 254 and provides areceived symbol stream. An RX spatial processor 240 performs receiverspatial processing on the N_(ap) received symbol streams from N_(ap)receiver units 222 and provides Nup recovered uplink data symbolstreams. The receiver spatial processing is performed in accordance withthe channel correlation matrix inversion (CCMI), minimum mean squareerror (MMSE), soft interference cancellation (SIC), or some othertechnique. Each recovered uplink data symbol stream is an estimate of adata symbol stream transmitted by a respective user terminal. An RX dataprocessor 242 processes (e.g., demodulates, deinterleaves, and decodes)each recovered uplink data symbol stream in accordance with the rateused for that stream to obtain decoded data. The decoded data for eachuser terminal may be provided to a data sink 244 for storage and/or acontroller 230 for further processing. The controller 230 may be coupledwith a memory 232

On the downlink, at access point 110, a TX data processor 210 receivestraffic data from a data source 208 for Ndn user terminals scheduled fordownlink transmission, control data from a controller 230, and possiblyother data from a scheduler 234. The various types of data may be senton different transport channels. TX data processor 210 processes (e.g.,encodes, interleaves, and modulates) the traffic data for each userterminal based on the rate selected for that user terminal. TX dataprocessor 210 provides Ndn downlink data symbol streams for the Ndn userterminals. A TX spatial processor 220 performs spatial processing (suchas a precoding or beamforming, as described in the present disclosure)on the Ndn downlink data symbol streams, and provides N_(ap) transmitsymbol streams for the N_(ap) antennas. Each transmitter unit 222receives and processes a respective transmit symbol stream to generate adownlink signal. N_(ap) transmitter units 222 providing N_(ap) downlinksignals for transmission from N_(ap) antennas 224 to the user terminals.

At each user terminal 120, N_(ut,m) antennas 252 receive the N_(ap)downlink signals from access point 110. Each receiver unit 254 processesa received signal from an associated antenna 252 and provides a receivedsymbol stream. An RX spatial processor 260 performs receiver spatialprocessing on N_(ut,m) received symbol streams from N_(ut,m) receiverunits 254 and provides a recovered downlink data symbol stream for theuser terminal. The receiver spatial processing is performed inaccordance with the CCMI, MMSE or some other technique. An RX dataprocessor 270 processes (e.g., demodulates, deinterleaves and decodes)the recovered downlink data symbol stream to obtain decoded data for theuser terminal. The decoded data for each user terminal may be providedto a data sink 272 for storage and/or a controller 280 for furtherprocessing

At each user terminal 120, a channel estimator 278 estimates thedownlink channel response and provides downlink channel estimates, whichmay include channel gain estimates, SNR estimates, noise variance and soon. Similarly, at access point 110, a channel estimator 228 estimatesthe uplink channel response and provides uplink channel estimates.Controller 280 for each user terminal typically derives the spatialfilter matrix for the user terminal based on the downlink channelresponse matrix Hdn,m for that user terminal Controller 230 derives thespatial filter matrix for the access point based on the effective uplinkchannel response matrix Hup,eff. Controller 280 for each user terminalmay send feedback information (e.g., the downlink and/or uplinkeigenvectors, eigenvalues, SNR estimates, and so on) to the accesspoint. Controllers 230 and 280 also control the operation of variousprocessing units at access point 110 and user terminal 120,respectively.

According to certain aspects of the present disclosure, the variousprocessors shown in FIG. 2 may direct the operation at an AP 110 and/oruser terminal 120, respectively, to perform various techniques describedherein, to determine whether LOS transmissions are utilized based ontraining signals and/or other processes for the techniques describedherein.

FIG. 3 illustrates various components that may be utilized in a wirelessdevice 302 in which aspects of the present disclosure may be practicedand that may be employed within the MIMO system 100. The wireless device302 is an example of a device that may be configured to implement thevarious methods described herein. The wireless device 302 may be anaccess point 110 or a user terminal 120.

The wireless device 302 may include a processor 304 which controlsoperation of the wireless device 302. The processor 304 may also bereferred to as a central processing unit (CPU). Memory 306, which mayinclude both read-only memory (ROM) and random access memory (RAM),provides instructions and data to the processor 304. A portion of thememory 306 may also include non-volatile random access memory (NVRAM).The processor 304 typically performs logical and arithmetic operationsbased on program instructions stored within the memory 306. Theinstructions in the memory 306 may be executable to implement themethods described herein. Processor 304 may, for example, perform ordirect operations 600 in FIG. 6 to make line of sight determinations,and/or other processes for the techniques described herein.

The wireless device 302 may also include a housing 308 that may includea transmitter 310 and a receiver 312 to allow transmission and receptionof data between the wireless device 302 and a remote location. Thetransmitter 310 and receiver 312 may be combined into a transceiver 314.A single or a plurality of transmit antennas 316 may be attached to thehousing 308 and electrically coupled to the transceiver 314. Thewireless device 302 may also include (not shown) multiple transmitters,multiple receivers, and multiple transceivers.

The wireless device 302 may also include a signal detector 318 that maybe used in an effort to detect and quantify the level of signalsreceived by the transceiver 314. The signal detector 318 may detect suchsignals as total energy, energy per subcarrier per symbol, powerspectral density and other signals. The wireless device 302 may alsoinclude a digital signal processor (DSP) 320 for use in processingsignals.

The various components of the wireless device 302 may be coupledtogether by a bus system 322, which may include a power bus, a controlsignal bus, and a status signal bus in addition to a data bus.

Aspects of the present disclosure may be used to determine whether LOStransmissions are utilized between devices based on training signals. Insome cases, the training signals may be transmitted as part of abeamforming (BF) training process (e.g., a beamforming trainingprocedure) according to, for example, the IEEE 802.11ad standard. The BFprocess is typically employed by a pair of millimeter-wave stations,e.g., a receiver and transmitter. Each pairing of the stations achievesthe necessary link budget for subsequent communication among thosenetwork devices. As such, BF training is a bidirectional sequence of BFtraining frame transmissions that uses sector sweep and provides thenecessary signals to allow each station to determine appropriate antennasystem settings for both transmission and reception. After thesuccessful completion of BF training, a millimeter-wave communicationlink is established.

The beamforming process solves one of the problems for communication atthe millimeter-wave spectrum, which is its high path loss. As such, alarge number of antennas are place at each transceiver to exploit thebeamforming gain for extending communication range. That is, the samesignal is sent from each antenna in an array, but at slightly differenttimes.

According to an exemplary embodiment, the BF process includes a sectorlevel sweep (SLS) phase and a beam refinement stage. In the SLS phase,one of the STAs acts as an initiator by conducting an initiator sectorsweep, which is followed by a transmit sector sweep by the respondingstation (where the responding station conducts a responder sectorsweep). A sector is either a transmit antenna pattern or a receiveantenna pattern corresponding to a sector ID. As mentioned above, astation may be a transceiver that includes one or more active antennasin an antenna array (e.g., a phased antenna array).

The SLS phase typically concludes after an initiating station receivessector sweep feedback and sends a sector acknowledgement (ACK), therebyestablishing BF. Each transceiver of the initiator station and of theresponding station is configured for conducting a receiver sector sweep(RXSS) reception of sector sweep (SSW) frames via different sectors, inwhich a sweep is performed between consecutive receptions and atransmission of multiple sector sweeps (SSW) (TXSS) or directionalMulti-gigabit (DMG) beacon frames via different sectors, in which asweep is performed between consecutive transmissions.

During the beam refinement phase, each station can sweep a sequence oftransmissions, separated by a short beamforming interframe space (SBIFS)interval, in which the antenna configuration at the transmitter orreceiver can be changed between transmissions. In other words, beamrefinement is a process where a station can improve its antennaconfiguration (or antenna weight vector) both for transmission andreception. That is, each antenna includes an antenna weight vector(AWV), which further includes a vector of weights describing theexcitation (amplitude and phase) for each element of an antenna array.

FIG. 4 illustrates a dual polarized patch element 400, in accordancewith certain aspects of the present disclosure. As shown in FIG. 4, asingle element of an antenna array may contain multiple polarizedantennas. Multiple elements may be combined together to form an antennaarray. The polarized antennas may be radially spaced. For example, asshown in FIG. 4, two polarized antennas (i.e. dual polarized antenna)may be arranged perpendicularly, corresponding to a horizontallypolarized antenna 410 and vertically polarized antenna 420.Alternatively or in addition, any number of polarized antennas may beused. One or both antennas of an element may also be circularlypolarized.

FIG. 5 is a diagram illustrating signal propagation 500 in animplementation of phased-array antennas. Phased array antennas useidentical elements 510-1 through 510-4 (hereinafter referred toindividually as an element 510 or collectively as elements 510). Thedirection in which the signal is propagated yields approximatelyidentical gain for each element 510, while the phases of the elements510 are different. Signals received by the elements are combined into acoherent beam with the correct gain in the desired direction. Anadditional consideration of the antenna design is the expected directionof the electrical field. In case the transmitter and/or receiver arerotated with respect to each other, the electrical field is also rotatedin addition to the change in direction. This requires that a phasedarray be able to handle rotation of the electrical field by usingantennas or antenna feeds that match a certain polarity and capable ofadapting to other polarity or combined polarity in the event of polaritychanges.

Information about signal polarity can be used to determine aspects ofthe transmitter of the signals. The power of a signal may be measured bydifferent antennas that are polarized in different directions. Theantennas may be arranged such that the antennas are polarized inorthogonal directions. For example, a first antenna may be arrangedperpendicular to a second antenna where the first antenna represents ahorizontal axis and the second antenna represents a vertical axis suchthat the first antenna is horizontally polarized and the secondvertically polarized. Additional antennas may also be included, spacedat various angles in relation to each other. Once the receiverdetermines the polarity of the transmission the receiver may optimizereception performance by matching the antenna to the received signal.

Example LOS Determination Based on Training Signals

As noted above, aspects of the present disclosure provide techniques fordetermining relative whether wireless devices are in a line of site(LOS) based on relative gain and/or phase of training signalstransmitted from antennas with different polarizations (e.g., horizontaland vertical). The techniques may be applied to any type of device whereLOS may be an important factor, such as devices using millimeter wavecommunications.

FIG. 6 illustrates example operations 600 that may be performed by awireless device for LOS detection, in accordance with certain aspects ofthe present disclosure.

Operations 600 begin at 602, by obtaining, via at least first and secondreceive antennas having different polarizations, first and secondtraining signals transmitted from a second apparatus via at least firstand second transmit antennas having different polarizations.

At 604, the wireless device determines, based on the first and secondtraining signals, one or more characteristics for differenttransmit-receive antenna pairs, each pair comprising one of the first orsecond transmit antennas and one of the first or second receiveantennas.

At 606, the wireless device generates, based on the characteristics, aline of sight (LOS) parameter indicative of whether a link path betweenthe first and second apparatus is LOS.

The operations 600 may be performed by any type of device having areceiver capable of measuring the phase and or gain of such a signal. Insome cases, such transmissions and measurements may be done during abeam training phase between a transmitter and receiver.

In some cases, transmitting and receiving only vertically orhorizontally polarized signals is inherent in the beam training phasesof various standards for millimeter wave communications, such as 802.1lad, in the sector level sweep (SLS) and beam refinement protocol (BRP)phases. During the BRP training phase using multi-polarization antenna,cross correlations of the transmitted signals may be identified whileantennas are switched on and off.

Information about signal polarity may be used to determine aspects ofthe transmitter of the signals. In certain aspects, the link pathbetween the transmitter and receiver may be determined based on signalpolarization. The phase, the gain, or both the phase and gain, may bemeasured by different antennas that are horizontally or verticallypolarized in order to detect an LOS path. For example, in the case of anLOS path, the vertically and horizontally polarized antennas shouldexhibit substantially identical pathloss from various environmentalconditions. Where the transmission is reflected, for example byenvironmental objects, the vertical and horizontally polarized signalsundergo different pathlosses due to varying reflection coefficients.

As a result, a parameter may be calculated based on a measureddifference or ratio between the signal received by the horizontally andvertically polarized antenna(s). This parameter may then be compared toa particular threshold. Where the parameter is equal to or above aparticular threshold, the signal path may be declared as a non-LOSsignal. Where the parameter is below the particular threshold, thesignal path may be declared a LOS signal.

In certain aspects, the transmitter sends training signals correspondingto each of a horizontal polarization and a vertical polarization one ata time in a given direction. The receiver then receives thetransmissions via horizontally polarized and vertically polarizedantennas. Once the receiver finds the average received power for eachpolarity, the receiver may compare the average received power.

For example, assuming an example where training signals are transmittedusing two transmit antennas (horizontal TX-H and vertical TX-V) and areceiver having two receive antennas (horizontal RX-H and vertical RX-V)may generate four characteristics. For example, a first characteristic,r1, may indicate the received signal strength of a transmission from thevertically polarized transmitting antenna, as received on the verticallypolarized receiving antenna. As such, each characteristic r1-r4 may beindicative of receive signal strength for each transmit-receive antennapair, r1-r4, such that:

r1=TX-V-->RX-V,

r2=TX-V-->RX-H,

r3=TX-H-->RX-V, and

r4=TX-H-->RX-H,

where -V describes a vertically polarized signal, -H a horizontallypolarized signal, TX describes a transmission, and RX describes areception.

A parameter may then be generated based on r1 and r4 and/or r2 and r3.Where the parameter indicates that the ratio (or difference) between r1and r4 and/or r2 and r3 is within a certain threshold (i.e. equal to orless than a threshold value), it may be assumed that there are nosubstantial reflections in the transmitted training signals and thereceiver may determine that there exists a LOS connection between thereceiver and the transmitter.

On the other hand, if the ratio (or difference) between the transmissionreceived via the horizontally and vertically polarized antennas exceed acertain threshold, then there is a non-LOS connection. The LOS parametermay also be compared against a second parameter generated to verify theresults. For example, when the LOS parameter is calculated based on r1and r4, this second parameter may be calculated based on r2 and r3, orbased on a different technique altogether.

In certain aspects, the thresholds or signals may be adjusted based onvarious factors to compensated for various environmental conditions.These factors may include known factors such as a cross-polarizationnumber, or polarization coefficients, antennas used, signal to noiseratio, or any other known factor. These factors may be transmitted bythe transmitter device. The receiver may receive an indication of thesefactors and use these factors to adjust the thresholds. Alternatively,the receiver may calculate, lookup, or otherwise obtain these factorswithout reference to the transmitter. According to certain aspects,different techniques for calculating LOS may be combined to make an LOSdetermination. For example, in some cases, LOS calculated based ontraining signals may be used to verify an LOS determination made byconventional means, such as PDP. As another example, an LOS parameter,calculated as described herein, may also be combined with determinationsmade by conventional means to further refine the LOS determination.

In certain aspects, after the receiver generates a LOS parameter,outputting the LOS parameter for transmission to the transmitter. Thetransmitter may also use this received LOS parameter to make a LOSdetermination, by, for example, comparing the LOS parameter to a certainthreshold which may or may not be the same threshold used by thereceiver.

In certain aspects, the determination as to whether LOS between atransmitter and receiver exists may be transmitted back to thetransmitter by the receiver as a part of positioning information.Additionally, LOS information may be passed up to an application layer,for example, for use by an application to help optimize receptionbetween the transmitter and receiver.

The various operations of methods described above may be performed byany suitable means capable of performing the corresponding functions.The means may include various hardware and/or software component(s)and/or module(s), including, but not limited to a circuit, anapplication specific integrated circuit (ASIC), or processor. Generally,where there are operations illustrated in figures, those operations mayhave corresponding counterpart means-plus-function components withsimilar numbering. For example, operations 600 illustrated in FIG. 6correspond to means 600A illustrated in FIG. 6A.

Means for obtaining (e.g., receiving) may comprise a receiver (e.g., thereceiver unit 254) and/or an antenna(s) 252 of the UT 120 illustrated inFIG. 2 or the receiver 312 and/or antenna(s) 316 depicted in FIG. 3.Means for transmitting and means for outputting may be a transmitter(e.g., the transmitter unit of transceiver 254) and/or an antenna(s) 252of the user terminal 120 illustrated in FIG. 2 or the transmitter (e.g.,the transmitter unit of transceiver 222) and/or antenna(s) 224 of accesspoint 110 illustrated in FIG. 2.

Means for generating, means for detecting, means for determining, meansfor obtaining, means for selecting, means for adjusting, means forprocessing, means for indicating, and/or means for applying may includea processing system, which may include one or more processors such asprocessors 260, 270, 288, and 290 and/or the controller 280 of the UT120 or the processor 304 and/or the DSP 320 portrayed in FIG. 3.

In some cases, rather than actually transmitting a frame a device mayhave an interface to output a frame for transmission. For example, aprocessor may output a frame, via a bus interface, to a radio frequency(RF) front end for transmission. Similarly, rather than actuallyreceiving a frame, a device may have an interface to obtain a framereceived from another device. For example, a processor may obtain (orreceive) a frame, via a bus interface, from an RF front end forreception.

According to certain aspects, such means may be implemented byprocessing systems configured to perform the corresponding functions byimplementing various algorithms (e.g., in hardware or by executingsoftware instructions) described above for determining the presence of aLOS transmission.

As used herein, the term “determining” encompasses a wide variety ofactions. For example, “determining” may include calculating, computing,processing, deriving, investigating, looking up (e.g., looking up in atable, a database or another data structure), ascertaining and the like.Also, “determining” may include receiving (e.g., receiving information),accessing (e.g., accessing data in a memory) and the like. Also,“determining” may include resolving, selecting, choosing, establishingand the like.

As used herein, a phrase referring to “at least one of” a list of itemsrefers to any combination of those items, including single members. Asan example, “at least one of: a, b, or c” is intended to cover a, b, c,a-b, a-c, b-c, and a-b-c, as well as any combination with multiples ofthe same element (e.g., a-a, a-a-a, a-a-b, a-a-c, a-b-b, a-c-c, b-b,b-b-b, b-b-c, c-c, and c-c-c or any other ordering of a, b, and c).

The various illustrative logical blocks, modules and circuits describedin connection with the present disclosure may be implemented orperformed with a general purpose processor, a digital signal processor(DSP), an application specific integrated circuit (ASIC), a fieldprogrammable gate array (FPGA) or other programmable logic device (PLD),discrete gate or transistor logic, discrete hardware components, or anycombination thereof designed to perform the functions described herein.A general-purpose processor may be a microprocessor, but in thealternative, the processor may be any commercially available processor,controller, microcontroller, or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration.

The steps of a method or algorithm described in connection with thepresent disclosure may be embodied directly in hardware, in a softwaremodule executed by a processor, or in a combination of the two. Asoftware module may reside in any form of storage medium that is knownin the art. Some examples of storage media that may be used includerandom access memory (RAM), read only memory (ROM), flash memory, EPROMmemory, EEPROM memory, registers, a hard disk, a removable disk, aCD-ROM and so forth. A software module may comprise a singleinstruction, or many instructions, and may be distributed over severaldifferent code segments, among different programs, and across multiplestorage media. A storage medium may be coupled to a processor such thatthe processor can read information from, and write information to, thestorage medium. In the alternative, the storage medium may be integralto the processor.

The methods disclosed herein comprise one or more steps or actions forachieving the described method. The method steps and/or actions may beinterchanged with one another without departing from the scope of theclaims. In other words, unless a specific order of steps or actions isspecified, the order and/or use of specific steps and/or actions may bemodified without departing from the scope of the claims.

The functions described may be implemented in hardware, software,firmware, or any combination thereof. If implemented in hardware, anexample hardware configuration may comprise a processing system in awireless node. The processing system may be implemented with a busarchitecture. The bus may include any number of interconnecting busesand bridges depending on the specific application of the processingsystem and the overall design constraints. The bus may link togethervarious circuits including a processor, machine-readable media, and abus interface. The bus interface may be used to connect a networkadapter, among other things, to the processing system via the bus. Thenetwork adapter may be used to implement the signal processing functionsof the PHY layer. In the case of a user terminal 120 (see FIG. 1), auser interface (e.g., keypad, display, mouse, joystick, etc.) may alsobe connected to the bus. The bus may also link various other circuitssuch as timing sources, peripherals, voltage regulators, powermanagement circuits, and the like, which are well known in the art, andtherefore, will not be described any further.

The processor may be responsible for managing the bus and generalprocessing, including the execution of software stored on themachine-readable media. The processor may be implemented with one ormore general-purpose and/or special-purpose processors. Examples includemicroprocessors, microcontrollers, DSP processors, and other circuitrythat can execute software. Software shall be construed broadly to meaninstructions, data, or any combination thereof, whether referred to assoftware, firmware, middleware, microcode, hardware descriptionlanguage, or otherwise. Machine-readable media may include, by way ofexample, RAM (Random Access Memory), flash memory, ROM (Read OnlyMemory), PROM (Programmable Read-Only Memory), EPROM (ErasableProgrammable Read-Only Memory), EEPROM (Electrically ErasableProgrammable Read-Only Memory), registers, magnetic disks, opticaldisks, hard drives, or any other suitable storage medium, or anycombination thereof. The machine-readable media may be embodied in acomputer-program product. The computer-program product may comprisepackaging materials.

In a hardware implementation, the machine-readable media may be part ofthe processing system separate from the processor. However, as thoseskilled in the art will readily appreciate, the machine-readable media,or any portion thereof, may be external to the processing system. By wayof example, the machine-readable media may include a transmission line,a carrier wave modulated by data, and/or a computer product separatefrom the wireless node, all which may be accessed by the processorthrough the bus interface. Alternatively, or in addition, themachine-readable media, or any portion thereof, may be integrated intothe processor, such as the case may be with cache and/or generalregister files.

The processing system may be configured as a general-purpose processingsystem with one or more microprocessors providing the processorfunctionality and external memory providing at least a portion of themachine-readable media, all linked together with other supportingcircuitry through an external bus architecture. Alternatively, theprocessing system may be implemented with an ASIC (Application SpecificIntegrated Circuit) with the processor, the bus interface, the userinterface in the case of an access terminal), supporting circuitry, andat least a portion of the machine-readable media integrated into asingle chip, or with one or more FPGAs (Field Programmable Gate Arrays),PLDs (Programmable Logic Devices), controllers, state machines, gatedlogic, discrete hardware components, or any other suitable circuitry, orany combination of circuits that can perform the various functionalitydescribed throughout this disclosure. Those skilled in the art willrecognize how best to implement the described functionality for theprocessing system depending on the particular application and theoverall design constraints imposed on the overall system.

The machine-readable media may comprise a number of software modules.The software modules include instructions that, when executed by theprocessor, cause the processing system to perform various functions. Thesoftware modules may include a transmission module and a receivingmodule. Each software module may reside in a single storage device or bedistributed across multiple storage devices. By way of example, asoftware module may be loaded into RAM from a hard drive when atriggering event occurs. During execution of the software module, theprocessor may load some of the instructions into cache to increaseaccess speed. One or more cache lines may then be loaded into a generalregister file for execution by the processor. When referring to thefunctionality of a software module below, it will be understood thatsuch functionality is implemented by the processor when executinginstructions from that software module.

If implemented in software, the functions may be stored or transmittedover as one or more instructions or code on a computer-readable medium.Computer-readable media include both computer storage media andcommunication media including any medium that facilitates transfer of acomputer program from one place to another. A storage medium may be anyavailable medium that can be accessed by a computer. By way of example,and not limitation, such computer-readable media can comprise RAM, ROM,EEPROM, CD-ROM or other optical disk storage, magnetic disk storage orother magnetic storage devices, or any other medium that can be used tocarry or store desired program code in the form of instructions or datastructures and that can be accessed by a computer. Also, any connectionis properly termed a computer-readable medium. For example, if thesoftware is transmitted from a website, server, or other remote sourceusing a coaxial cable, fiber optic cable, twisted pair, digitalsubscriber line (DSL), or wireless technologies such as infrared (IR),radio, and microwave, then the coaxial cable, fiber optic cable, twistedpair, DSL, or wireless technologies such as infrared, radio, andmicrowave are included in the definition of medium. Disk and disc, asused herein, include compact disc (CD), laser disc, optical disc,digital versatile disc (DVD), floppy disk, and Blu-ray® disc where disksusually reproduce data magnetically, while discs reproduce dataoptically with lasers. Thus, in some aspects computer-readable media maycomprise non-transitory computer-readable media (e.g., tangible media).In addition, for other aspects computer-readable media may comprisetransitory computer-readable media (e.g., a signal). Combinations of theabove should also be included within the scope of computer-readablemedia.

Thus, certain aspects may comprise a computer program product forperforming the operations presented herein. For example, such a computerprogram product may comprise a computer-readable medium havinginstructions stored (and/or encoded) thereon, the instructions beingexecutable by one or more processors to perform the operations describedherein. For certain aspects, the computer program product may includepackaging material.

Further, it should be appreciated that modules and/or other appropriatemeans for performing the methods and techniques described herein can bedownloaded and/or otherwise obtained by a user terminal and/or basestation as applicable. For example, such a device can be coupled to aserver to facilitate the transfer of means for performing the methodsdescribed herein. Alternatively, various methods described herein can beprovided via storage means (e.g., RAM, ROM, a physical storage mediumsuch as a compact disc (CD) or floppy disk, etc.), such that a userterminal and/or base station can obtain the various methods uponcoupling or providing the storage means to the device. Moreover, anyother suitable technique for providing the methods and techniquesdescribed herein to a device can be utilized.

It is to be understood that the claims are not limited to the preciseconfiguration and components illustrated above. Various modifications,changes and variations may be made in the arrangement, operation anddetails of the methods and apparatus described above without departingfrom the scope of the claims.

What is claimed is:
 1. A first apparatus for wireless communications,comprising: a first interface for obtaining, via at least first andsecond receive antennas having different polarizations, first and secondtraining signals transmitted from a second apparatus via at least firstand second transmit antennas having different polarizations; aprocessing system configured to: determine, based on the first andsecond training signals, one or more characteristics for differenttransmit-receive antenna pairs, each pair comprising one of the first orsecond transmit antennas and one of the first or second receiveantennas, and generate, based on one or more characteristics, aparameter indicative of whether a link path between the first and secondapparatuses is line of sight (LOS).
 2. The first apparatus of claim 1,further comprising a second interface for outputting the parameter fortransmission to the second apparatus.
 3. The first apparatus of claim 1,wherein: the first and second receive antennas comprise at least onevertically polarized receive antenna and at least one horizontallypolarized receive antenna; and the first and second transmit antennascomprise at least one vertically polarized transmit antenna and at leastone horizontally polarized transmit antenna.
 4. The first apparatus ofclaim 1, wherein the one or more characteristics comprise receive powerof training signals transmitted and received via a given one of thetransmit-receive antenna pairs.
 5. The first apparatus of claim 1,wherein the one or more characteristics comprise receive phase oftraining signals transmitted and received via a given one of thetransmit-receive antenna pairs.
 6. The first apparatus of claim 1,wherein the one or more characteristics comprise: a first characteristicfor a first transmit-receive antenna pair is determined based on thefirst training signal as received on the first receive antenna; and asecond characteristic for a second transmit-receive antenna pair isdetermined based on the second training signal as received on the secondreceive antenna.
 7. The first apparatus of claim 6, wherein theprocessing system is configured to indicate, via the parameter, that thelink path between the first and second apparatuses is LOS if adifference or a ratio between the first and second characteristics isequal to or below a threshold value.
 8. The first apparatus of claim 7,wherein the first and second characteristics and the threshold value areadjusted based on a factor.
 9. The first apparatus of claim 8, whereinthe factor is based on at least one of a cross-polarization number orpolarization coefficients.
 10. The first apparatus of claim 8, whereinthe factor is based on at least an indication received from the secondapparatus.
 11. The first apparatus of claim 6, wherein the one or morecharacteristics further comprise: a third characteristic for a thirdtransmit-receive antenna pair is determined based on the first trainingsignal as received on the second receive antenna; and a fourthcharacteristic for a fourth transmit-receive antenna pair is determinedbased on the second training signal as received on the first receiveantenna.
 12. The first apparatus of claim 11, wherein the parameter isgenerated based on at least one of: the first and secondcharacteristics; or the third and fourth characteristics.
 13. The firstapparatus of claim 12, wherein the processing system is configured toindicate, via the parameter, that the link path between the first andsecond apparatuses is LOS if a difference or a ratio between the firstand second characteristics or a difference or a ratio between the thirdand fourth characteristics is equal to or below a threshold value. 14.The first apparatus of claim 1, wherein the first and second trainingsignals are received as a part of a beamforming training procedure. 15.The first apparatus of claim 1, wherein: the different polarizations ofthe first and second transmit antennas correspond to horizontal andvertical polarizations.
 16. The first apparatus of claim 1, wherein: thedifferent polarizations of the first and second receive antennascorrespond to horizontal and vertical polarizations.
 17. The firstapparatus of claim 1, wherein: at least the first and second receive andtransmit antennas comprise a dual polarized antenna.
 18. The firstapparatus of claim 1, wherein at least one of the first or secondantenna is circularly polarized.
 19. A method for wirelesscommunications by a first apparatus, comprising: obtaining, via at leastfirst and second receive antennas having different polarizations, firstand second training signals transmitted from a second apparatus via atleast first and second transmit antennas having different polarizations;determining, based on the first and second training signals, one or morecharacteristics for different transmit-receive antenna pairs, each paircomprising one of the first or second transmit antennas and one of thefirst or second receive antennas; and generating, based on one or morecharacteristics, a parameter indicative of whether a link path betweenthe first and second apparatuses is line of sight (LOS).
 20. The methodof claim 19, further comprising outputting the parameter fortransmission to the second apparatus.
 21. The method of claim 19,wherein: the first and second receive antennas comprise at least onevertically polarized receive antenna and at least one horizontallypolarized receive antenna; and the first and second transmit antennascomprise at least one vertically polarized transmit antenna and at leastone horizontally polarized transmit antenna.
 22. The method of claim 19,wherein the one or more characteristics comprise receive power oftraining signals transmitted and received via a given one of thetransmit-receive antenna pairs.
 23. The method of claim 19, wherein theone or more characteristics comprise receive phase of training signalstransmitted and received via a given one of the transmit-receive antennapairs.
 24. The method of claim 19, wherein the one or morecharacteristics comprise: a first characteristic for a firsttransmit-receive antenna pair is determined based on the first trainingsignal as received on the first receive antenna; and a secondcharacteristic for a second transmit-receive antenna pair is determinedbased on the second training signal as received on the second receiveantenna. 25-31. (canceled)
 32. The method of claim 19, wherein the firstand second training signals are received as a part of a beamformingtraining procedure.
 33. The method of claim 19, wherein: the differentpolarizations of the first and second transmit antennas correspond tohorizontal and vertical polarizations.
 34. The method of claim 19,wherein: the different polarizations of the first and second receiveantennas correspond to horizontal and vertical polarizations. 35-36.(canceled)
 37. A first apparatus for wireless communications,comprising: means for obtaining, via at least first and second receiveantennas having different polarizations, first and second trainingsignals transmitted from a second apparatus via at least first andsecond transmit antennas having different polarizations; means fordetermining, based on the first and second training signals, one or morecharacteristics for different transmit-receive antenna pairs, each paircomprising one of the first or second transmit antennas and one of thefirst or second receive antennas; and means for generating, based on oneor more characteristics, a parameter indicative of whether a link pathbetween the first and second apparatuses is line of sight (LOS). 38-55.(canceled)
 56. A wireless station, comprising: at least first and secondreceive antennas having different polarizations; a receiver forreceiving, via the first and second receive antennas, first and secondtraining signals transmitted from a second apparatus via at least firstand second transmit antennas having different polarizations; and aprocessing system configured to: determine, based on the first andsecond training signals, one or more characteristics for differenttransmit-receive antenna pairs, each pair comprising one of the first orsecond transmit antennas and one of the first or second receiveantennas, and generate, based on one or more characteristics, aparameter indicative of whether a link path between the first and secondapparatuses is line of sight (LOS).